The city of Tandil in Argentina has a population of more than 100,000 and it seems that every one of them knows Juan Martín Del Potro. Since he won the US Open last September Del Potro's popularity has gone through the roof, to such an extent that he can barely leave his house without being mobbed by well-wishers.

For some megastars, as Del Potro is fast becoming in Argentina, never having a minute to himself when he is at home would cause them to leave the country, get as far away as possible. But Del Potro, 21, is a quiet, unassuming man, if that's possible for someone who stands at 6ft 6in tall.

"When I go out with my friends, if people come up to me, everyone has good intentions and means well," he says, taking a break from preparations for his first-round match at the ­Australian Open, to be played tomorrow.

"Everyone says many, many, good things to me, and it's an extra motivation. Christmas was good, with many friends, but now they come to my house because I cannot walk around. But I feel very, very normal there."

Tandil and Del Potro are not ­normal, though. Maybe it is something in the water or something in the meat the locals consume, but this relatively small city has produced a host of top sportsmen, including Mauro Camoranesi, the Juventus footballer. Tennis is the sport at which Tandil has really excelled, ­producing six professional players, including Mariano Zabaleta and Juan Mónaco, both of whom have won ATP Tour titles, and Del Potro ­himself. Even more remarkable is that their ­development has been guided by one man, Marcelo Gómez, who, Del Potro says, simply focused on the basics.

"He is more like a father than a coach," Del Potro says. "When I was young, I travelled with him and he was like another father and that's very important when you are young. I still speak to him every day, he is a very good person. I spoke to him before the US Open final. My parents are friends with him."

Del Potro is at pains to suggest that he is no different to anyone else. He has a close-knit family and is modest, almost to the point where you wonder how he can cope with the cut-throat nature of professional sport. This, lest we forget, is the man who destroyed Rafael Nadal in the semi-finals at Flushing Meadows and then beat the world No1, Roger Federer, in a remarkable final to clinch his first grand slam title. Being a grand slam champion brings with it responsibility and Del Potro admits he can no longer stay in the shadows.

"I am a quiet man," he says. "When I am working, I know this is my work so I can be focused for three hours, four hours, or whatever, and then outside I am a person like you or the children playing soccer in the street. If I have the possibility to say something to make them happy, I will do it. This is the most lovely thing after the US Open – the kids, especially, have a very good ­rapport with me."

Like almost all Argentinians, Del Potro loves football, and he is also very keen on rugby union. Del Potro's father was a handy rugby player but though Del Potro Jr was shoved in the second row, it didn't suit him. "No, I can't play," he says. "I don't like the contact."

He watches as much rugby as he can, though, and is immensely proud that Agustín Pichot became the first rugby player ever to win Argentina's sportsman of the year award in December.

"We have the best soccer player [Lionel Messi of Barcelona] and the best rugby player," he said. "For Argentinian sport it is very good, especially for the kids. Pichot is a great person, a great professional; he was always the captain of the team and in Argentina he has a very good reputation."

Though Del Potro was never good enough to make it professionally as a footballer – "When I was young I was good at it but now I can't move, I can't run for 90 minutes" – he has formed lasting friendships with several of the top players, including the Manchester City striker Carlos Tevez and Tandil's own Camoranesi, who is a dual national and plays internationally for Italy.

Tevez came to watch Del Potro during the ATP World Tour finals at London's O2 in November, where Del Potro made the final, and the pair gave the crowd a laugh when they knocked up at the end of one match, although on that evidence, Tevez would be well-advised not give up his day job. "You didn't like his tennis?" Del Potro says with a laugh.

His other football friends are handier with a racquet, though. The Inter midfielder Esteban Cambiasso is "very good", he says, while Martín Palermo, the Argentina striker whose goal against Peru kept them alive in their qualifying campaign for this summer's World Cup, is "a very good lefty". He adds: "I met Paolo Maldini in Italy – he plays very well."

Del Potro's win at Flushing Meadows confirmed what most people had realised for a long time, that here was a star in waiting. His forehand is enormous and his height has always been an advantage, but he has worked hard on his fitness and his win over Federer dispelled any questions about his stamina. He beat Federer again as he reached the final in London and his confidence is high going into the first grand slam event of the year.

A twinge in his right wrist gave him a little scare here but he says he will be ready to go tomorrow, when he begins his title attempt against American Michael Russell. Having overtaken Andy Murray to take the world No4 spot, Del Potro is one of the clear favourites to win the title. He may well be hoping that Nadal takes care of Murray in the quarter-finals because, while he has enjoyed recent success against the Spaniard, he has won only once against the Scot in their six meetings.

You would think that his US Open win would have convinced him that he deserves to be mentioned in the same breath as Federer and Nadal, but Del Potro is not ready to make that leap of faith just yet.

"Roger has more experience than me, he plays great tennis," Del Potro says. "Rafa, too, he can beat everyone. Of course, I am fighting with them, ­especially at the end of last season, but I think they are still the favourites. I think I am maybe still below them and many players are in the same state."

Surely, though, he feels more confident within himself, having won his first grand slam title before he turned 21? "After the final I felt more relaxed. I'd won my first grand slam, my favourite grand slam and no one could say anything about my tennis or my physical [prowess] because I beat Roger in five sets in five hours. But then the pressure comes again, the sponsors, the people, the tournaments, everything. Everyone comes to watch you and think it's a little more pressure.

"When I am warming up and I hear 'US Open champion' that's great. Maybe it gives you more confidence. But if he breaks your serve in the first game, then it's real life."